Raw wool contains three main contaminants: dirt, water soluble contamination (wool suint) and wool grease, which together account for about 20-30% of the fleece weight. Typically, the wool grease content of the raw fleece may be around 3 to 6%.
Wool scouring is performed to convert dirty greasy wool into clean scoured wool. The first step of raw wool scouring is to remove the impurities present in the wool by suitable physical or chemical means. Conventionally, the process of cleaning/scouring of animal fibers, for example woolscouring, involves the submersion of greasy fibers in a series of aqueous bowls. The initial bowls, heated to temperatures of 50-70° C. contain a surfactant composition to remove the greasy residues of the animal fibers, for example wool. The method involves a further number of wash bowls to remove any surfactant residue or dirt residue remaining on the animal fibers, for example wool. The wash bowls may be either hot or cold and may also include further chemicals such as for example hydrogen peroxide or organic acids to further improve the quality of the animal fibers, for example wool being scoured. These chemicals are not however designed to remove or affect the grease which is removed in the initial bowls. Once the raw wool has been processed through the bowls containing surfactant solution, the remaining spent surfactant solution contains emulsified wool grease.
Wool grease is a complex mixture containing mostly of esters of long chain fatty acids with long chain alcohols and sterols. Wool grease can be processed into lanolin, wool wax alcohols (lanolin alcohol), wool wax acids (lanolin acids), lanolin derivatives and wool wax alcohol derivatives. Lanolin is a multi-functional commercially highly valuable product and is used for example in the production of soap and cosmetics. Mixed wool-wax alcohols can be formed by hydrolysis of the esters followed by solvent extraction of the alcohols. Mixed wool-wax alcohols are used for example in medicinal products and toiletries. It is therefore desirable to remove the wool grease from the emulsion-scouring liquor as effectively as possible. Wool grease also includes cholesterol which is used for example in cosmetic products and industrial products.
One conventional method for removing wool grease from the emulsion-scouring liquor is the centrifugal method. The centrifugal method involves passing the emulsion-scouring liquor through a desludging centrifuge. The desludging centrifuge provides a wool-grease concentrate stream which is rich in lanolin. A second conventional method is the acid-cracking method.
Conventionally, nonylphenol ethoxylates have been used as the surfactant in the wool scouring process to remove natural greases from wool. There is however, concern that nonylphenol ethoxylates may break down and release nonylphenol into the environment. Nonylphenol is difficult to break down and it bio-accumulates in the environment. Nonylphenol has been found to be highly toxic to aquatic organisms and can cause long term adverse effects in the aquatic environment. Furthermore, it is undesirable for nonylphenol to be present within the products produced from refined woolgrease.
The use of a primary alcohol ethoxylate has also been disclosed for wool scouring. It has however been found that the use of a primary alcohol ethoxylate results in reduced efficiency in terms of wool grease removal from wool.
Furthermore, the use of conventional surfactants has been found to provide grease residues which are difficult to separate using the centrifugal method due to the stability of the emulsions.
There is therefore a need for a method of cleaning animal fibers, for example wool, which uses a more environmentally friendly surfactant. There is also a need for a method or a surfactant with improved efficiency for grease removal from animal fibers, for example wool. There is also a need for a method or surfactant which provides a grease residue from the animal fibers, in which the grease residue has reduced stability and as a result provides easier separation of the grease, for example requiring a lower splitting speed during the centrifugal method.